Epilepsy is characterized by a tendency to recurrent seizures that can lead to loss of awareness or consciousness, disturbances of movement, sensation (including vision, hearing, and taste), autonomic function, mood, and mental function. Epilepsy afflicts 1-2% of the population of the developed world. The mean prevalence of active epilepsy (i.e., continuing seizures or the need for treatment) in developed and undeveloped countries combined is estimated to be 7 per 1,000 of the general population, or approximately 40 million people worldwide. Studies in developed countries suggest an annual incidence of epilepsy of approximately 50 per 100,000 of the general population. However, studies in developing countries suggest this figure is nearly double at 100 per 100,000.
Vagus nerve stimulation (VNS) has been applied with partial success in patients with refractory epilepsy. In this procedure, an implantable pulse generator is implanted in the patient's thorax, and an electrode lead is routed from the generator to the left vagus nerve in the neck. Helix-shaped stimulation and indifferent electrodes are attached to the vagus nerve via an invasive surgical process that requires the carotid sheath to be fully exposed. Based on a number of studies, approximately 5% of patients undergoing VNS are seizure-free, and an additional 30-40% of patients have a greater than 50% reduction in seizure frequency. However, VNS may lead to significant side effects. The vagus nerve provides parasympathetic innervation to the cardiac tissue, and thus VNS may lead to bradycardia, arrhythmia, or even graver cardiac side effects. In fact, VNS systems are often only used on the left vagus nerve, as the right vagus nerve contributes significantly more to cardiac innervation. Additionally, VNS may interfere with proper opening of the vocal cords, which has led to hoarseness and shortness of breath in a significant number of VNS patients.
As another example of a nerve disorder, recent estimates suggest that the number of U.S. men with erectile dysfunction may be near 10-20 million, and inclusion of individuals with partial erectile dysfunction increases the estimate to about 30 million. Electrical stimulation can be used to treat erectile dysfunction. The targets of electrical stimulation are the cavernous nerves. The cavernous nerves run bilaterally between the prostate and the rectum as they course from the sacral spinal cord to the corpora cavernosa in the penis. Near the rectum the nerves form more of a plexus than a coherent nerve, and they are interlaced with small arteries and veins as well as fatty tissue. This collection of small nerve fibers, arteries, and veins can be referred to as the neurovascular bundle.